The copending application of A. Y. Feldblum et al., Ser. No. 08/024,035, filed Mar. 1, 1993, now U.S. Pat. No. 5,286,338, Feb. 15, 1994 and the patent of Derkits, U.S. Pat. No. 5,079,130, granted Jan. 7, 1992, both hereby incorporated herein by reference, describe a method for making microlens arrays comprising the steps of forming an array of photoresist elements on a silica substrate, melting the elements to cause them to have curved or dome-shaped surfaces, and thereafter solidifying the elements. The photoresist elements and the substrate are then subjected to reactive ion etching, that is, etching by a reactive gas in which the reaction is enhanced by applied radio frequency power. The photoresist elements cause differential etching of the substrate such that, after all of the photoresist has been etched away, the dome shapes of the original photoresist elements are replicated in the silica substrate.
The application points out that the technique is useful for making arrays of microlenses which can be used as a unit, or from which individual or discrete lenses can be selected for use. If discrete lenses are to be made, the array must be cut by any of a variety of methods to separate the individual lenses. Mechanical sawing of the array may be impractical because it may produce microcracks in the lenses that could interfere with their function. Also, it is sometimes desirable, for optimizing optical characteristics, to produce individual microlenses each having a circular outer periphery, and making the required circular cuts can be difficult. The Feldblum et al. technique for making microlenses would be much more practical for making discrete microlenses if methods for separating an array into individual elements, especially circular elements, could be simplified.